A means for widening a light-sensitive wavelength region of a silver halide emulsion and making a sensitivity higher has been well-known as a spectral sensitization technique. As for spectrally sensitizing dyes applicable to satisfy the purpose of the above-mentioned technique, a great number of compounds such as a cyanine dye and a merocyanine dye have been known so far.
Such a spectrally sensitizing dye as mentioned above has to widen the light-sensitive wavelength region of a silver halide emulsion and satisfy the various requirements such as given below.
1) A spectrally sensitizing region is to be suitable;
2) A spectrally sensitizing efficiency is to be high;
3) A fog production, a gamma variation and/or the like are not to affect photographic characteristic curves;
4) Photographic characteristics such as fogginess are not to be varied when aging a silver halide photographic light-sensitive material containing a sensitizing dye (particularly when preserving it under the conditions of a high temperature and a high humidity.);
5) Any color contamination is not to be produced by diffusion of a sensitizing dye in one layer to another layer having any different sensitive wavelength region; and
6) After completing each of developing, fixing and washing step, a light-sensitive dye is washed off and any color stain is not to be produced off.
However, any spectrally sensitizing dyes having so far been disclosed still have been unable to reach a level fully satisfying the above-mentioned requirements.
Further, recently the film processing speed has entered into a super-rapid mass-processing age, and diagnostic equipments such as a CT and an MRT are each used in a process for exclusive use directly connected to a photographing equipment. In the case of a super-rapid processing (for not longer than 45 seconds) and in the case of a small amount of replenishing a developing chemical, a further improvement of processability has been demanded, because a residual color has been liable to produce.
The known light-sensitive dyes effectively capable of spectrally sensitizing a red-light wavelength region include, for example; a complex cyanine dye and a complex merocyanine dye disclosed in Belgian Patent No. 541,245, U.S. Pat. Nos. 2,493,747, 2,743,272 and 3,335,010, French Patent No. 2,113,248 and German Patent Nos. 1,024,800, 2,153,570 and 2,300,321 and Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP OPI Publication) No. 3-171135/1991; a cyanine dye disclosed in JP O.P.I. Publication Nos. 49-11121/1974, 51-33622/1976, 51-115821/1976, 51-115822/1976, 58-72937/1983, 61-203446/1986, 2-256045/1990 and 3-15042/1991; a merocyanine dye disclosed in U.S. Pat. Nos. 2,493,747, 2,493,748 and 2,519,001 and JP OPI Publication Nos. 51-106422/1976 and 59-214030/1984. In some part of these dyes, a residual color stain has been tried to reduce it by introducing a water-solublilizing group into the molecules thereof, however, there have still been such a problem that the reduction of the residual color stains have not been satisfactory, or that a sensitivity variation has been liable to occur when lowering a spectrally sensitized sensitivity or when aging a coating solution and, therefore, the dyes have still not been satisfied.
The dyes described in European Patent Nos. 363,104 and 363,107 have also been proved to display the effect of improving a residual color stain. However, when aging a light-sensitive material spectrally sensitized by making use of these dyes, there has raised such a problem that the photographic characteristics thereof are varied.
JP OPI Publication Nos. 54-18726/1979, 59-135461/1984 and 62-246045/1987 disclosed each such a technique that a spectral sensitivity is enhanced and a residual color stain is reduced by making use of the above-mentioned dye and a supersensitizer in combination. However, these techniques have still been on an unsatisfiable level and, therefore, a further improvement has been demanded.
In recent years, the following means has been getting popularized, in which an image digital or video signal for radiation-diagnostic use such as MRI, X-ray CT and digital X-ray diagnoses is taken in and then processed, and the resulting processed signal is expressed imagewise on a silver halide photographic light-sensitive material by scanning with a laser beam, so that the image is served as a transparent image so as to perform a diagnosis.
In a recording system in which a laser beam is used, an image quality has been made high as a semiconductive laser has been getting popularized and it has, therefore, been demanded for a silver halide photographic light-sensitive material for laser-beam source use, which is high in sensitivity and stable in characteristics in aging. At present, in addition to the above, there have demanded for a silver halide photographic light-sensitive material for laser-beam source use having stable characteristics each compatible to the range from a 630 nm light-source typified by a conventional He-Ne laser to a 680-650 nm semiconductive laser having recently been put in practical use.
However, with a light-sensitive material spectrally sensitized by a conventional red-sensitizing dye, a resulting image density is varied by the difference of time between a point of time when an exposure is made and a point of time when a development is made. The image density variation is produced because a latent image produced by exposure is not stable (that is, the progression and regression of a latent image are relatively great). Therefore, a handling convenience is worsened from an exposure through a development.
In the recording systems in which the above-mentioned laser-beam source is used, the period or the environment during from the point of time when making an exposure to the point of time when making a development are different between a system in which a laser-imager and an automatic processor are directly connected together and another system in which a laser-imager and an automatic processor are separately arranged to each other. Therefore, the difference results in a density variation which is problematic.